We've recently bought an old Crown, and are currently removing the floor due to rot issues. I had planned on laying down a layer of 3/4 " plywood and then putting fir flooring over the top of that. In the demolition process, i've discovered that there is some type of 1/2" asphalt backed fiberboard that is sandwiched in between the top layer of 3/4' ply and the bottom layer of 3/8" ply. This was all screwed to metal struts at various intervals- no metal floor except around the wheel wells. I'm wondering about the purpose and and importance of this fiberboard- sound and/or heat insulation? Could this material be much more effective than the same thickness of plywood and solid fir? An important consideration is that the engine is in the middle of the bus underneath the floor, so sound deadening seems fairly important...
Another item i am unsure of is the undercoating on the bottom layer of plywood. I had thought of doing an epoxy coat on the bottoms and sides of the underlayment plywood, at least around the wheel wells. Is this overkill? Is there a cheaper exterior paint that would be appropriate?
-lastly, everything in our bus is fastened with an annoying breed of safety screw-the head is like a many pointed gear, and the auto parts store sells no bit to to drive them. We've been removing them with vise grips, a laborious and sometimes ineffective process, as they strip easily. Is there some specialty bit available? I sure hope so.